Apparatus for blow molding with active ingredient in blowing gas

ABSTRACT

Articles, such as containers, can have their barrier properties improved either by using a small percentage of fluorine or other materials in the gas that is used at the blowing station of an injection blow molding machine. Some of these materials, such as fluorine are a hazard to operators of the machine. This invention encloses the operational stations so that the blowing gas mixture cannot escape into the atmosphere of the shop where the blow molding machine is operating. An inert gas such as nitrogen is mixed with the fluorine gas, and the enclosing housing is purged when the machine is shut down at the end of a run.

PRIOR ART

Methods for producing extrusion blow molded thermoplastic articleshaving improved barrier properties are disclosed in U.S. Pat. No.3,862,284, issued Jan. 21, 1975. Examples of gasses that can be mixedwith the gas used for blowing containers are described; and so are theproportions for improved results in retaining solvents in thecontainers. U.S. Pat. No. 2,724,860 discloses blowing the parison whilestill in a molten state with a compressed fluid or blowing gas, toconform the parison with the contour of the surrounding mold cavity.

U.S. Pat. No. 2,811,468 discloses a method of treating polyethylene filmand bottles that have been thoroughly cleaned with two percent fluorineand the balance nitrogen, air, freon and the like at temperatures notexceeding fifty degrees C. for a period of five minutes to three hours.

BACKGROUND AND SUMMARY OF INVENTION

The problem with which this invention is concerned is the protection ofmachine operators from the noxious gasses used to improve the barrierproperties with certain types of blow molding machines. It is much moredifficult to provide such protection in injection blow molding machineshaving successive operational stations angularly spaced around the axisof a table, in that core rods extend successively into molds at theangularly spaced operational stations around the axis of anintermittently indexible head that carries core rods, usually groups ofcore rods.

The process for making molded thermoplastic articles having improvedbarrier properties according to U.S. Pat. No. 3,862,284 does not makethe blow molded articles by processes that have the large output ofinjection blow molding machines, and it is an object of this inventionto use injection blow molding apparatus to reduce the cost of thearticles of patent '284 by increasing the output of plastic containershaving improved barrier properties and thereby reducing the unit cost.This invention converts an ordinary injection blow molding machine, withsuccessive operational stations, into an improved apparatus for makingcontainers having better barrier properties.

The principal object of the invention is to enclose the stations of aninjection blow molding machine within a chamber in which the stationsare shut off from the working environment of machine operators. Thefinished containers are discharged from the molding machine, preferablyafter being flushed by nitrogen or other inert gas to eliminate most ofthe hazardous gas.

Other objects, features, and advantages of the invention will appear orbe pointed out as the description proceeds.

DESCRIPTION OF THE DRAWING

In the drawing, forming a part hereof, in which like referencecharacters indicate corresponding parts in all of the views;

FIG. 1 is a diagrammatic top plan view, partly in section, of aninjection blow molding machine having, but not limited to, threeoperational stations providing visibility of the stations but shieldingeach station to prevent the operator from breathing fumes which mayescape from successive stations;

FIG. 2a and 2b are sectional views taken on the lines 2a --2a and2b--2b, respectively, of FIG. 1;

FIG. 3 is a diagrammatic view with the gas shield of FIG. 1, taken onthe section line 3--3 of FIG. 1 and with other parts shown in elevationand diagrammatically; and

FIG. 4 is a diagrammatic view showing a modification of the structure ofFIG. 3 and showing the way in which poisonous gas is purged from theblown containers.

DESCRIPTION OF PREFERRED EMBODIMENT

FIG. 1 is a plan view, partly in section, of a blow molding machine 10having, but not limited, to, three operational stations including aninjection station 12, a blow station 14, and a stripper station 16. Anindexing head 18 notates about a center 20. The indexing head 18 hasthree faces 22 which move intermittently through angles of 120° to bringcore rods 24 into working relationship with the operational stations12-14-16. Large molding machines have a plurality of cores extendingfrom each face of the head 18 but for purposes of illustration only onecore rod 24 is shown for each face 22.

The injection station 12 has an injection mold 26, best shown in FIG.2a; in conjunction with a core rod 24, the cavity 27 of this mold isdefined by and between a fixed mold section 26a which is secured to afixed portion of the injection station 12, and an upper movable moldsection 26b which is attached to a frame 28; frame 28 moves up and downto open the mold 26 whenever the core rod 24 is to be shifted from oneoperational station to the next.

Referring again to FIG. 1, a reciprocating or continuously rotatingscrew plasticizer 30 is movable in the direction of its length towardand from the mold 26 so as to bring the discharge end 32 of theplasticizer to the inlet end 34 of the mold 26 so that molten materialfrom the plasticizer 30 can be discharged into the injection mold cavity27; the cavity 27 is formed by a clearance between core rod 24 andcavity walls of mold sections 26a-26b, and cavity 27 is concentric withthe axis of the mold. Molten plastic from the plasticizer 30 fills thiscavity, which extends to a core rod neck ring 36.

When the mold 26 at the injection mold station opens, the indexing head18 rises to lift the core rod 24 and its parison sufficiently to clearthe lower mold section 26a (FIG. 2a) so the indexing head 18 cantransport the core rod 24 to the next operational station, namely, theblowing station 14, where, after indexing head 18 moves downward, anupper mold section 26d (FIG. 2b) moves downward into contact with alower mold section 26c to close the blow mold 26c-26d.

In addition to fluorine, other reactive gasses such as sulphur dioxide,carbon monoxide, carbon dioxide, chlorine, bromine, and mixtures ofthese gasses can be used in place of fluorine, though theireffectiveness in improving the barrier properties of the material of theparison differ. In any event, the gas mixture can be prepared externallyfrom the machine and maintained at an accurate level for the process,simplifying the blowing process.

As with conventional injection blow molding equipment, the walls of theblow mold should be maintained at relatively low temperature so that theplastic of the blown parison will harden quickly after making contactwith the cavity wall of the blow mold. This is essential in order tomaintain high production with injection blow molding machines becausethe blown article should be cooled to a solid state and removed (as afinished container 52) from the blow mold as soon as possible.

When the blow mold at station 14 opens and the head 15 indexes 120° ,the core rod 24 and its blown parison are brought to the stripperstation 16, where an upstanding stripper plate 50 first engages thecontainer 52 at the container neck and then pushes it from the core rod24. While holding container 52 by its neck, plate 50 next moves to theright in FIG. 3 and then displaces from upright to a horizontalposition, as shown in dotted lines 50', thereby placing the finishedcontainer 52 in an upright position. A purge tube 53 is lowered throughthe open top of the container 52, and a stream of nitrogen from thepurge tube 53 displaces the flourine from the container 52. Tube 53 alsopushes the container 52 free of the stripper plate 50, allowingcontainer 52 to fall on a spring loaded trap door 55. The weight of thecontainer 52 opens the door 55 so that the container 52 can fall clearof the molding machine and may be carried away by a conveyor 56.

FIG. 4 shows a modification of the stripper station already described inconnection with FIG. 3. In FIG. 4, the plate 50 moves container 52toward the right, and the plate 50 remains vertical. Instead of rotatingthrough an angle of 90° as in FIG. 3, the plate 50 of FIG. 4 moves thecontainer 52 across a baffle 88. When the plate 50 has reached the limitof its travel, the container 52 is positioned, as shown in dotted lines52' in FIG. 4, with the shoulder of the container beyond the top of thebaffle 88.

A motor 86 reverses the direction of movement of the plate 50 so thatthe plate moves toward the left in FIG. 4. The upper end of the baffle88 holds the container 52 against movement when plate 50 starts itsreturn movement toward the left, and this causes plate 50 to disengagefrom the neck of the container 52. The container slides down the baffle88 into a well 90 which is slightly larger in cross section than thecontainer 52, and is thereby reoriented, with its neck up and on avertical axis, as shown in FIG. 4. The tube 53 then descends, as in FIG.3, and into the interior of the container 52, and a blast of nitrogenfrom the tube 53 flushes out the noxious gas from the container 52' thenitrogen blast also exerts a downward force on the container and therebycauses a trap door 92, under the container, to open and permit thecontainer to fall by gravity onto a conveyor or chute or into a largeshipping box.

It will be understood that a program control 78 controls a motor 80which intermittently rotates the indexing head 18 and also controls amotor 82 which raises and lowers the indexing head 18 in accordance withthe cycle of the machine.

If the poisonous gas is not removed from the blown parison (container50) at the blowing station, there are two other methods by which thecontainer can be purged of poisonous gas, without need for purging eachcycle; these two other methods are a result of scrubber action, as willlater appear. It is a feature of the invention that a housing or cover,preferably transparent, shall cover the head 18 and all of theoperational stations 12-14-16. In FIGS. 1 and 3, this housing isidentified 64, and in the modification of FIG. 4 it is identified 64'.

A gas scrubber 72 removes gas from the space enclosed by the housing 64(64'), in the event of any leakage of gas within the housing 64 (64').Any hazardous gas that escapes at the blow station or the stripperstation is confined under the housing 64 (64') and is eventually carriedto the gas scrubber 72 by a blower 76.

In the apparatus and process of this invention it is not necessary topurge the apparatus after each blowing operation. The treating gas inthe blow gas system can remain in the system all the time that theapparatus is running. The purging for hazardous gas from the hood formedby the housing 64 (64') that enclose the operational stations can bedone when the apparatus is shut down. It can be done manually by simplycutting off the blow gas supply and turning on a burst of nitrogen.

In an invention of this kind, there are occasional leaks in the system,as when a hole is accidentally blown in a container. The gas whichescapes from the ruptured container flows into the immediate area whichis enclosed by the housing (64'). This housing is an enclosure but it isordinarily not sealed. The flourine gas is controlled by the fact theblower 76 (FIG. 4) which pulls air from the housing enclosure creates anegative pressure in the enclosure so that air comes into the areawherever there might be a leak in the housing 64. This keeps theflourine from getting out.

In order to prevent too much air from entering the enclosure andrequiring the use of a much larger scrubber, due to oxygen from theambient atmosphere, it is preferable to meter in a small flow ofnitrogen to cut down on air leakage into the housing 64. This lowers thehumidity in the area because the dew point of nitrogen is -200° F.; alower temperature is maintained within the housing 64 (64') because thenitrogen is so cold.

The scrubber is supported from the housing 64 (64'), or it may beremotely mounted; it discharges to the atmosphere after cleaning theair.

The housing 64 (64') is actually a guard that must be raised to work onor set up molds. When the apparatus is running, the housing 64 (64')rests on a gasket on top of a table that extends under all theoperational stations of the machine.

What is claimed is:
 1. Injection blow molding apparatus comprising aplurality of operational stations including an injection station, ablowing station, a stripper station, and an indexing head around whichthe stations are located and spaced at equal angles and from which corerods extend into the respective stations, a housing spaced from andenclosing the blowing station and the stripper station to shut off gasthat is used in the blowing station and the stripper station from theambient atmosphere outside of the housing, apparatus for blowingcontainers at the blowing station with gas containing hazardous fumes,means for venting to space within said housing the gas containing thehazardous fumes from the blown container and from objects blown at theblowing station by gas containing the hazardous fumes, and means forcollecting from said space the gas containing the fumes and forsupplying the hazardous gas to the blowing station for subsequentblowing operations where the blown container is filled with thehazardous gas mixture.
 2. The injection blow molding apparatus describedin claim 1 characterized by means for venting said hazardous fumes fromsaid housing at the end of a production run and a scrubber in which thehazardous fumes are collected.
 3. The injection blow molding apparatusdescribed in claim 1 characterized by means for supplying flourine gasand another gas, as a mixture for blowing containers at the blowingstation, the fluorine gas being the hazardous gas that is separated fromthe other gas after being used in the blowing station to expand aparison on a core rod at the blowing station.
 4. The injection blowmolding apparatus described in claim 1 characterized by the housingsurrounding the full extent of the indexing head and enclosing all ofthe operational stations so that all of the core rods remain enclosedwithin said housing at all times when the injection blow moldingapparatus is in operation.
 5. The injection blow molding apparatusdescribed in claim 1 characterized by said last-defined means includinga scrubber for separating the hazardous gas from other gas.
 6. Theinjection blow molding apparatus described in claim 1 characterized bymeans for supplying at said blowing station a mixture of nitrogen withenough fluorine to chemically improve the inside surfaces of containersblown by the mixed nitrogen and fluorine gas at the blowing station,said housing maintaining the nitrogen and fluorine mixture of gasseswithin said space and within a blowing circuit of the apparatus when theblow molding apparatus is in operation, and means for purging said spaceand therefore said enclosed operational stations of hazardous gas toprotect operating personnel when operation of the machine is shut downafter a run.
 7. The injection blow molding apparatus described in claim1 characterized by the blowing station having a mold shaped to blowcontainers, means for supplying a mixture of nitrogen and fluorine tothe blowing station, means for supplying additional nitrogen to blowncontainers to purge the fluorine from the interior of such containersand into said space before they pass beyond the stripper station, and ascrubber through which the fluorine and nitrogen are passed from saidhousing.
 8. The injection blow molding apparatus described in claim 1characterized by the stripper station including means for holding eachof the blown containers as it comes from the blowing station to thestripper station, and means at the stripper station for inserting aprobe into successive blown containers to purge the hazardous gastherefrom and into said space.
 9. The injection blow molding apparatusdescribed in claim 8 characterized by means for supplying said probewith a mixture of one to ten percent of fluorine in a nitrogenatmosphere.
 10. The injection blow molding apparatus described in claim1 characterized by the blown containers being blown while on the corerods at the blowing station, and means for discharging the containersfrom the core rods at the stripper station, said discharging meansincluding a trap door under the core rods at the stripper station and inposition for blown containers to be discharged from the space withinsaid housing.
 11. The injection blow molding apparatus described inclaim 1 characterized by a cooled blowing mold at the blowing station sothat the parison within the mold is quickly cooled and hardened whenblown into contact with the walls of the blowing mold.